The invention relates to a low migration, odor and swelling sheet-fed offset printing ink which is suitable for the production of food wrapping.
On the one hand, sheet-fed offset printing inks are known in the prior art which can be described as low as to odor and flavor. These inks contain low odor components such as hard resins, hydrogenated mineral oil cuts, synthetic aromatic oils, alkyd resins, in particular such with a low iodine number of xe2x89xa630 g J2/100 g, and dialkyl ether such as di-n-dodecyl ether, di-n-undecyl ether, allyl-n-octyl ether, n-hexyl-n-undecyl ether as a vehicle.
However, mass transfers of these inks to the filling material can occur, the mass transfers being assessable according to the law of diffusion. However, the German food law prohibits any mass transfer, except for components which are safe with regard to health, odor and flavor and which are technically unavoidable. Migration of the liquid components in inks of the prior art can occur, however, which can further cause the unwanted aspect of the so-called swelling. As a result of migration, in particular thin packing films, i.e. films under 30 xcexcm, can be affected by warping of the film in form of wrinkling and waves. These warps are irreversible and optically and technically non-acceptable.
Furthermore, so-called anti-swelling inks are known in the prior art which have a vehicle composition free of mineral oil. The serious disadvantage of these inks is, however, that the low-viscous vehicle components can have considerable migration potentials. Therefore, it is possible that mass transfers occur in primary packing which can disadvantageously change the odor and flavor of the filling material, in particular of the food. Such transfers are treated, for example, according to Swiss law as impurities (xe2x80x9cDecree on Food Additives and Ingredientsxe2x80x9dxe2x80x94Fremd- und Inhaltsstoffe-verordnung, FIVxe2x80x94of Jun. 26, 1996). According to the German food law, too, it is applicable to the wrapping of food and semiluxuries that changes in odor and flavor of the filling material by the wrapping are to be avoided (xc2xa731 LMBG, section 1).
Therefore, it was an object of the invention to provide sheet-fed offset printing inks which are low in migration and odor as well as low in swelling, and which, therefore, do not cause any unwanted changes in odor and flavor of the wrapping and which obey the migration values stipulated by law, respectively.
Changes in odor and flavor of the wrapped goods caused by printing inks are tested according to DIN 10955, testing of packaging and wrapping material for food. In this connection, the values must be smaller than 2 in order to meet the requirements mentioned.
The object of the invention is solved by an offset printing ink which comprises a colophony-modified phenolic resin (A) and/or a maleic resin (B) and/or a modified hydrocarbon resin (C) and/or a colophony resin ester (D),which is characterized in that it comprises one or more water-insoluble fatty acid ester(s) of multivalent alcohols with a high steric spatial requirement and/or of ethinols as a solvent for the resin(s).
Spatial requirement is to be understood as the three-dimensional steric measurement of molecules. In this connection, the steric measurements of the esters being employed as a solvent can amount to lmax of from 2.0 to 7.0 nm in diameter and to a Vmean of from 1.0 to 21.0 nm3 in volume, the indicated values referring to the maximum length of the molecules.
Furthermore, in a preferred embodiment, the offset printing ink according to the invention comprises multifunctional allyl esters of multivalent organic acids. These allyl esters are capable of oxidative drying and during the drying process they do not produce any fragments which cause sensory impairments of the wrapped food. In the oxidative drying process, a cross-linking takes place and this results in a stable printing ink film. This process of oxidative cross-linking of the printed ink is caused by the salts of organic acids of cobalt and/or manganese in concentrations of 0.05-0.2% which are contained therein.
Preference is given to allyl esters of multivalent organic acids with an acid number of 2-20 mg KOH/g (DIN 55 936), a iodine number of 50-120 g J2/100 g (DIN 55 936) and a viscosity of 0.5-300 mPaxc2x7s measured at 20xc2x0 C. and 50 l/s as well as with a molecular weight Mw of 300-10000.
Furthermore, an offset printing ink is preferred which comprises a polyallyl ether, additionally. Its function basically corresponds to the one of the multifunctional allyl esters.
With the addition of multifunctional allyl esters and polyallyl ethers, respectively, it is possible to achieve the mechanical resistance which is required in the technical application for the wrapping of food and semiluxuries and which has so far been achieved in a majority of cases only by coating, so that this can be dropped.
Furthermore, an offset printing ink according to the invention is preferred which is free of mineral oil.
These inks are free of substances with a high migration potential. The resins and special fatty acid esters with their high steric spatial requirements contained in the vehicles of the inks and/or the fatty acid esters of ethinols are coordinated so that, also in the case of primary packing, the mass transfer to the food is so much reduced that it distinctly remains under the limit values stipulated by law. Moreover, in the case of direct contact between the printed ink and, for example, a polypropylene packing film there is almost no change in the dimension due to the prevention of a mass transfer according to the invention. This was hitherto caused by a migration to the polymer matrix which is called swelling of films.
Therefore, with the inks according to the invention it is the first time that the advantageous properties low in odor, migration and swelling have been achieved simultaneously in sheet-fed offset printing inks. Therefore, these inks are particularly suited for the production of food wrappings under employment of, for example, cardboard and paper.
Moreover, a very substantial advantage of the offset printing ink according to the invention is the fact that it is based on renewable raw materials.
Furthermore, an offset printing ink according to the invention is particularly preferred in which the fatty acids of the fatty acid esters comprise a carbon chain of 6-26, in particular of 8-26, carbon atoms. The fatty acids can be saturated or unsaturated fatty acids. The following fatty acids are given as examples: octadecene acid, linolic acid, linolenic acid, elaeostearic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, arachic acid, dodecanoic acid, hexanoic acid, octanoic acid, decanoic acid, and docosenoic acid. These fatty acids can be purified by means of distillation before esterifying them.
An offset printing ink according to the invention is preferred in which the multivalent alcohols are selected from trimethylolpropane, pentaerythritol, dipentaerythritol, sorbitol and 2-butyl-2-ethyl-1,3-propanediol. Furthermore, an offset printing ink according to the invention is preferred in which the fatty acid esters of multivalent alcohols have an acid number between 5 and 20 mg KOH/g (DIN 53402), a iodine number between 0 and 150 g J2/100 g (DIN 55936) and a viscosity between 20 and 500 mPaxc2x7s (DIN 53229). The multivalent alcohols are polyesterified or completely esterified.
Examples for water-insoluble fatty acid esters which are employed according to the invention are: pentaerythritol tetracaprate, dipentaerythritol hexacaprate, pentaerythritol tetradocoseate, and dipentaerythritol hexadocoseate.
The employment of natural vegetable oils, i.e. of the corresponding triglycerides, cannot solve the problem posed. With the employment of the specified offset printing ink according to the invention it was unexpectedly possible to solve the problem for the first time.
Furthermore, an offset printing ink according to the invention is preferred which is characterized in that that the resins have a molecular weight Mw of 5000-120000, an acid number of 10-40, a hydroxyl number of 20-70 and a melting range of 120-190xc2x0 C. In this case, the measuring of the melting range is carried out according to the capillary method.
The resins are to behave sensorially neutral and to dissolve in the mentioned fatty acid esters or their mixtures without the employment of co-solvents. Moreover, the resins are to be compatible with the mentioned fatty acid esters or their mixtures. The compatibility of a resin solution and a vehicle, respectively, is defined by the hexane number (HEZ). The compatibility is to be in a HEZ-range between 0 and +20.
Resins with a viscosity of 10-90 Paxc2x7s at 40% in mineral oil (Company Haltermann PKW-F 6/9) and with a viscosity of 20-100 Paxc2x7s at 40% in mineral oil (Company Haltermann PKW-f 6/9 ar), respectivelyxe2x80x94each measured at 50 l/s and at a temperature of 20xc2x0 C.xe2x80x94have proved to be particularly suited and thus preferred.
Furthermore, resins with a turbidity point of 55-150xc2x0 C. at 10% in mineral oil (Company Haltermann PKW-F 6/9 af new) and with a turbidity point of 50-150xc2x0 C. at 10% in mineral oil (Company Haltermann PKW-F 6/9), respectively, have proved to be particularly suited.
An offset printing ink in which the resins (A):(B) have a quantitative ratio of 33-76:24-67 as well as an offset printing ink in which the resins (A):(B):(C) have a quantitative ratio of 22-51:23-46:16-33 have proved to be advantageous.
Particularly advantageous and thus preferred is an offset printing ink according to the invention in which the resins (A) and (B) as well as the fatty acid ester of multivalent alcohols (E) have a quantitative ratio of 17-36:13-32:45-70 as well as an offset printing ink according to the invention in which the resins (A), (B), (C) and (D) as well as the fatty acid ester (E) have a quantitative ratio of (A):(B):(C):(D):(E) of 0-45:0-32:0-24:0-19:38-70.
The production of the offset printing inks is carried out in a fashion which is known per se.
The ratio of viscosity to tackiness of the offset printing inks should be in the range of 50-120 Paxc2x7s (50 l/s, 20xc2x0 C.) to 8-14 (26xc2x0 C.; rate of measurement 200 rpm; 1.3 m3 ink), the tackiness being measured by means of the Prxc3xcfbau-Inkomat (name of the measuring apparatus) of the company Dxc3xcrner.
The rheological data of the offset printing inks are adjusted to the requirements of technical application and to the substrates for printing in a way which is known per se.